Carrier Test Page

Duchenne/Becker Muscular Dystrophy

What is Duchenne/Becker Muscular Dystrophy?

Duchenne Muscular Dystrophy (DMD) is an inherited disorder that affects skeletal and heart muscles. Skeletal muscle loss causes major weakness that affects movement. Symptoms appear in early childhood and rapidly worsen. Children are typically wheelchair dependent by 12 years of age. Heart problems usually appear after age 18 years. A variable degree of intellectual disability is possible in affected males. Becker muscular dystrophy (BMD) is milder and symptoms are more varied, with muscle weakness appearing later in childhood or adolescence and progressing at a slower rate. Most males affected with DMD die before thirty years of age due to heart or respiratory failure, while males with BMD have a life expectancy into their forties or older. DMD and BMD are caused by pathogenic variants in the DMD gene.

How is Duchenne/Becker Muscular Dystrophy inherited?

DMD is inherited in an X-linked recessive manner. This type of inheritance requires the presence of one copy of a pathogenic variant in the gene located on the X-chromosome for males to be affected. When the pathogenic variant is inherited from the unaffected carrier mother, the male child will have the genetic disease. There is a 50% chance that a baby will inherit the pathogenic variant from the mother; females who inherit the pathogenic variant will be carriers, males who inherit the pathogenic variant will be affected. In DMD, 2/3 of the cases are inherited pathogenic variants, the remaining 1/3 result from new pathogenic variants in the male and are not inherited. In BMD, 90% of mothers are carriers of a pathogenic variant.

What does it mean to be a carrier?

Carrier females may develop a variable degree of muscle weakness and cramping, and are at risk to develop heart problems in adulthood. Routine cardiac evaluation is recommended.